Boilers

ABSTRACT

Described herein is a steam boiler comprising a furnace defined by water tube walls, i.e. gas tight walls made of a plurality of tubes connected to one another by fins, a plurality of downcomer tubes which connect an upper steam drum to at least one lower distribution header which feeds at least some and preferably all of the tubes of the water tube walls, and a convection bank of evaporating tubes, the tubes of which are connected directly to the downcomer tubes before the latter enter the distribution header. The advantage of this is that an expensive lower water drum is not required and if the downcomer tubes form one water tube wall of the boiler one can also avoid some heat insulation.

United States Patent Akturk et al.

BOILERS inventors: Nuri Uygun Akturk, Cheltenham; Ronald Arthur Ashdown, Redhill, both of England Foster Wheeler Corporation, Livingston, NJ.

Filed: Mar. 15, 1974 Appl. No.: 451,711

[73] Assignee:

Foreign Application Priority Data Mar. l5, I973 United Kingdom.r............. l26l7/73 US. Cl. 122/478; l22/4l2; l22/42l Int. Cl. F22G 7/14; F22D l/02 Field of Search 122/235 R, 336, 412, 421,

[ June 10, 1975 2,68l,047 6/l954 Dalin et al. 122/421 X 2,704,534 3/l955 Dalin et al. 3,098,469 7/l963 Row 122/478 [57] ABSTRACT Described herein is a steam boiler comprising a furnace defined by water tube walls, i.e. gas tight walls made of a plurality of tubes connected to one another by fins, a plurality of downcomer tubes which connect an upper steam drum to at least one lower distribution header which feeds at least some and preferably all of the tubes of the water tube walls, and a convection bank of evaporating tubes, the tubes of which are connected directly to the downcomer tubes before the latter enter the distribution header. The advantage of this is that an expensive lower water drum is not required and if the downcomer tubes form one water tube wall of the boiler one can also avoid some heat insulation.

7 Claims, 2 Drawing Figures PATENTEDJUNm I975 1: Cum 7 sass: 1

PATENTEDJUH 10 I975 S'HEF? FIG. 2

BOILERS This invention relates to the industrial steam boilers and more particularly to non-reheat-steam boilers.

BACKGROUND TO THE INVENTION One form of conventional steam boiler comprises an upper steam drum and a lower water drum connected to one another by tubes to provide a convection bank of tubes. Adjacent to the convection bank is situated a furnace-region defined by tube walls, the tubes of which extend between the upper and lower drums. I-Iot gases in the furnace are arranged to pass through a superheater near the roof of the furnace into the convection bank, and thence into a duct where the gases pass through economisers.

In another form of steam boiler, the upper and lower drums and the convection bank are arranged in a high position relative the furnace, an additional header being provided at the base of the furnace and being connected by tubes which line the walls of the furnace enclosure to the steam drum. As in the above type of boiler hot gases pass from the furnace through the con vection bank and into economisers positioned in a duct.

Both of the above types of steam boiler, which operate at low pressure and which provide relatively low super heat, have a number of disadvantages.

The water and steam drums are of relatively large diameter and have to be of relatively thick material because of the large number of tube penetrations; therefore these drums are expensive.

Also, both types of boiler have limitations in their design flexibility. The first form described above has to be increased in size and duty by axial increase in size of the water and steam drums due to the problems of increasing the distance between the drum centres, and thus the lengths of the down and consequently their costs are increased. The second form of boiler can be expensive due to the fact that the water and steam drums, and convection bank, are held in a high position by supporting means.

Both types of boiler have the disadvantage that extensive heat insulated gas ducting has to be provided.

The invention has been made with all these points in mind and has as an object a reduction in the number of expensive large diameter drums or headers.

BRIEF DESCRIPTION OF THE INVENTION According to the invention there is provided a steam boiler comprising a furnace enclosure defined by water tube walls, a plurality of downcomer tubes which connect an upper steam drum to a lower distribution header for feeding at least some and preferably all of the tubes of the water tube walls, and a convection bank of evaporating tubes, the tubes of which are connected directly to the downcomer tubes before the downcomer tubes enter the distribution header.

A steam boiler according to the invention avoids many of the disadvantages mentioned above. The steam boiler can have only a single large diameter drum and thus the cost of the steam boiler can be reduced. Also the design is such that a single general design can readily be adapted for a range of loads by increasing or decreasing the size of the convection tube bank and this naturally reduces the cost of the boiler because the drum and water tube walls can be of a standard design.

Furthermore, the downcomer tubes can be in the form of a water tube wall forming one wall of the boiler and extensive heat insulated gas ducting can be avoided.

The steam boiler of the invention is preferably a natural circulation boiler.

In a preferred embodiment of the invention, the convection bank of evaporating tubes are in the form of a screen. Thus the tubes of the convection bankcan have an inclined leg across which the gases pass as they flow along the convection section and a substantially upright leg across which the gases pass as they enter the convection section from the furnace. Superheaters can be provided in the furnace, suitably screened from the direct radiation, and economisers can be provided below the convection bank of evaporating tubes in the convection chamber. Hot gases from the furnace will thus pass through the superheaters, into the convection bank of tubes, and thence through the economisers to a flue gas outlet.

Another advantage of the invention stems from the fact that there can be fewer tube penetrations in the upper steam drum since a plurality of tubes in the convection bank of tubes can be connected to a single downcomer tube. A number of tubes in the convection bank of tubes can be connected to a single return riser which is connected to the upper steam drum. The steam drum can thus be made of a thinner material and costs can be reduced.

By the term "water tube wall" as used herein we mean gas tight walls which comprise a plurality of tubes connected to one another by fins.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be description, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic upright sectional elevation of a steam boiler according to the invention; and

FIG. 2 is an enlarged detail showing this convection bank.

DESCRIPTION OF THE PREFERRED EMBODIMENT The steam boiler 10 shown in the drawing has an outer casing 11. The boiler has a furnace chamber 12 and a convection pass 14 to which the hot combustion gases pass from the chamber 12. The chamber 12 is defined by water tube walls 16, 18, 20 and 22 and water tube side walls 27.

The convection pass 14 is defined by a water tube wall of the downcomer tubes 25, the tube wall 16, and side water tube walls 27. The pass 14 contains a convection bank of evaporating tubes 26 which are arranged in the form of a screen. Each tube is in two parts, a lower inclined leg 260 leading from the downcomer tubes 25 and an upright leg 26b leading to return tubes 24. The legs 26a of the tubes of the convection bank of tubes are connected to the downcomer tubes 25 before the latter enter a lower distribution header 28 near the base of the boiler.

Near the top of the boiler is positioned an upper steam drum 30 to which the downcomer tubes 25 are connected.

The tubes of the convection bank 26 are connected to return tubes 24 and these tubes lead to the steam drum 30. Seals 32 and 34 are provided to maintain a gas tight seal in the convection chamber 14.

In order to provide superheated steam, a pendant superheater 40 is provided in the furnace 12 near the upper water tube wall 20. The superheater is shielded from furnace radiation by the water tube wall 16, the tubes of which are connected to the lower distribution header 28 and to a roof header 44 which is connected in turn to the steam drum 30. Near their top, the tubes of the tube wall 16 are separated into two groups 16a and 16b and the fins removed so as to allow the gases to pass from the chamber 12 to the convection pass 14.

The superheater 40 is composed of serpentine shaped tubes 41 extending between a final outlet header 50 and a primary inlet header 52 which is connected through the tube 54 to the steam drum 30. Intermediate the headers 50 and 52 are a primary outlet header 56 and final inlet header 58 which are connected to a desuperheater header 60.

The lower distribution header 28, which is fed by the downcomer tubes 25, is connected to the tubes of the water tube wall 16 and to the tubes of the water tube walls 18, 20, and 22. The latter tubes are connected to the roof header 44.

The tubes of the side water tube walls 27 defining the sides of the furnace enclosure 12 are connected to upper side wall headers and lower side wall headers 64 which are connected to the steam drum 30 and lower distribution header 28, respectively.

The tubes 27 of the side water tube walls 27 defining the convection pass 14 are connected to upper headers 66 and lower headers 67, the upper headers leading to the steam drum 30.

Situated in the convection chamber 14 below the bank of evaporating tubes 26 are banks 68 of economiser tubes.

The boiler is held by a framework of girders 70, and is supported on blocks 72.

Air enters the boiler through an inlet 74 and passes to the furnace chamber 12 via the burner (not shown) positioned in parts 76 formed by bending some of the tubes of the wall 18. Hot gases produced in the furnace pass through the superheater 40 into the convection pass 14, thus passing through the screen formed by the convection bank of evaporating tubes 26. The gases then pass through the economisers 68 to a flue outlet 80.

The downcomer tubes feed the convection bank of evaporating tubes 26 and thus the use of a convec tional convection bank extending between upper and lower drums is avoided. The distribution header 28 is very much smaller than a normal water drum and thus costs can be reduced. Furthermore, the upper steam drum has far fewer tube penetrations than normal steam drums because many of the tubes lead to intermediate headers which in turn lead to the drum, and consequently can be made of thinner metal, thus again reducing costs.

The design of steam boiler of the invention is very flexible since the size of the convection bank of evaporating tubes can be increased without affecting the overall size of the boiler.

Although the terms water" and steam are used herein, they are to be construed as including any suitable liquid and its vapour, unless the cotext specifically requires otherwise.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What 1 claim is:

l. A natural circulation steam boiler comprising:

a furnace enclosure,

water tube walls defining said furnace enclosure, said walls having upper and lower ends,

an upper steam drum,

tube means connecting said upper ends to said steam drum,

a lower distribution header,

tube means connecting said lower distribution header and said lower ends,

downcomer tubes extending between said drum and said header, and,

a convection bank of evaporating tubes, said tubes being connected directly to said downcomer tubes at locations on said downcomer tubes between said drum and said header,

whereby the provision of a lower water drum in said steam boiler is obviated.

2. A steam boiler according to claim 1 wherein said downcomer tubes are in the form of a water tube wall.

3. A steam boiler according to claim 1 wherein said convection bank of evaporating tubes are positioned within a convection pass down which hot combustion gases from said furnace enclosure pass, the tubes of said bank of evaporating tubes having an inclined leg joined directly to said downcomer tubes and a substantially upright leg past which said gases pass as they enter said convection pass from said furnace enclosure.

4. A steam boiler according to claim 3 further comprising intermediate tubes to which said upright legs are joined to said steam drum, a plurality of upright legs being joined to said intermediate tubes which are therefore fewer in number than said tubes in said bank of evaporating tubes.

5. A steam boiler according to claim 3 further comprising a superheater positioned adjacent the entrance of said convection pass, said superheater being shielded from radiant heat by a water tube wall separating said furnace enclosure and said convection pass.

6. A steam boiler comprising:

a. a furnace enclosure in which hot combustion gases are produced,

b. an upright convection pass down which said hot combustion gases pass from said furnace enclosure,

c. upright water tube walls forming sides for said furnace enclosure and said convection pass,

a water tube wall forming the floor, front and roof of said furnace enclosure,

e. an intennediate water tube wall forming the rear of said furnace enclosure and the front of said convection pass, the tubes of said intermediate wall at the top of said wall being arranged so that said combustion gases can pass through said wall from said furnace enclosure to the top of said convection pass,

f. a rear water tube wall defining the rear of said convection pass,

g. an upper steam drum,

h. a lower distribution header connected by said rear water tube wall to said steam drum, whereby the tubes of said rear wall acts as downcomers,

vection pass; the tubes of said bank having lower ends joined directly to said downcomer tubes at a position intermediate said drum and said header.

7. A steam boiler according to claim 6 additionally comprising a superheater being, said superheating shielded by said intermediate wall from furnace radiant heat and being positioned adjacent the top of said intermediate wall. 

1. A natural circulation steam boiler comprising: a furnace enclosure, water tube walls defining said furnace enclosure, said walls having upper and lower ends, an upper steam drum, tube means connecting said upper ends to said steam drum, a lower distribution header, tube means connecting said lower distribution header and said lower ends, downcomer tubes extending between said drum and said header, and, a convection bank of evaporating tubes, said tubes being connected directly to said downcomer tubes at locations on said downcomer tubes between said drum and said header, whereby the provision of a lower water drum in said steam boiler is obviated.
 2. A steam boiler according to claim 1 wherein said downcomer tubes are in the form of a water tube wall.
 3. A steam boiler according to claim 1 wherein said convection bank of evaporating tubes are positioned within a convection pass down which hot combustion gases from said furnace enclosure pass, the tubes of said bank of evaporating tubes having an inclined leg joined directly to said downcomer tubes and a substantially upright leg past which said gases pass as they enter said convection pass from said furnace enclosure.
 4. A steam boiler according to claim 3 further comprising intermediate tubes to which said upright legs are joined to said steam drum, a plurality of upright legs being joined to said intermediate tubes which are therefore fewer in number than said tubes in said bank of evaporating tubes.
 5. A steam boiler according to claim 3 further comprising a superheater positioned adjacent the entrance of said convection pass, said superheater being shielded from radiant heat by a water tube wall separating said furnace enclosure and said convection pass.
 6. A steam boiler comprising: a. a furnace enclosure in which hot combustion gases are produced, b. an upright convection pass down which said hot combustion gases pass from said furnace enclosure, c. upright water tube walls forming sides for said furnace enclosure and said convection pass, d. a water tube wall forming the floor, front and roof of said furnace enclosure, e. an intermediate water tube wall forming the rear of said furnace enclosure and the front of said convection pass, the tubes of said intermediate wall at the top of said wall being arranged so that said combustion gases can pass through said wall from said furnace enclosure to the top of said convection pass, f. a rear water tube wall defining the rear of said convection pass, g. an upper steam drum, h. a lower distribution header connected by said rear water tube wall to said steam drum, whereby the tubes of said rear wall acts as downcomers, i. connection means for joining the lower ends of said side, front and intermediate water tube walls to said distribution header and upper ends of said side, front and intermediate water tube walls to said steam drum, whereby water flows by natural circulation from said drum to said hearder via said rear water tube wall, up said side, front and intermediate water tube walls to said drum, and j. a convection bank of evaporating tubes in said convection pass; the tubes of said bank having lower ends joined directly to said downcomer tubes at a position intermediate said drum and said header.
 7. A steam boiler according to claim 6 additionally comprising a superheater being, said superheating shielded by said intermediate wall from furnace radiant heat and being positioned adjacent the top of said intermediate wall. 